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7/25/2019 Genetics and DNA
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Coordination Complexes in Biological Systems
Porphyrin
Porphyrins are heterocyclic macrocycles composed
of four modified interconnected pyrrole subunits.
They form coordination complexes with metal ionsand are found in biological systems.
Chlorophyll c2 Heme B Cobalamin
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Hemoglobin and Myoglobin
Notice that the hemoglobin is essentially a tetramer of myoglobin. (There are four
myoglobin like units in hemoglobin.)
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Oxygenated and Deoxygenated Forms
N
H
N
HN
N
Proximal Histidine (F8)
Distal Histidine (E7)
Fe
F helix
E helix
NH
N
Proximal Histidine (F8)
Fe
O
O
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The Role of the Protein
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Hemoglobin and Myoglobin
Fe-O-O = 150
Raman Spectra gives o-o at 1105 cm-1, indicating that the complex should be in asuperoxide state
o-o (cm
-1
) 1560 1100 850-740
O2
O2 O
22
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Coordination Environment of Fe
HN
N
NH
N
Fe2+
dxz dyz
dxy
dz2
dx2-y2
Total unpaired electrons = 4, S = 2
Deoxygenated form is high-spin andparamagnetic
Total unpaired electrons = 1, S = 1/2
Oxygenated form is low-spin
The magnetic moment of Fe3+ and the
superoxide radical involves in anti-
ferromagnetic coupling and the oxygenated
complex is not paramagneticNH
N
Fe3+
O
O
dxz dyz
dxy
dz2
dx2-y2
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Ferromagnetism
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Antiferromagnetism
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Hemoglobin and Myoglobin
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Bohr Effect
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Hemoglobin and Myoglobin
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